In digital imaging, the dynamic range of a complementary metal-oxide-semiconductor (CMOS) sensor may, at times, be insufficient to accurately represent outdoor scenes in a single image. This may be especially true in the more compact sensors which may be used in mobile devices, such as in the camera on a mobile telephone. For example, a typical sensor used in a mobile device camera may have a dynamic range of approximately 60-70 dB. However, a typical natural outdoor scene can easily cover a contrast range of 100 dB between brighter areas and areas with shadows. Because this dynamic range is greater than the dynamic range of a typical sensor used in a mobile device, detail may be lost in images captured by mobile devices.
One method which has been used to compensate for this lack of dynamic range is to combine two or more frames into a single image with a higher dynamic range. For example, two of more frames with different exposure lengths may be combined into a single image. However, one problem with previous techniques for combining multiple frames has been a signal-to-noise ratio discontinuity between frames of different exposure lengths. One method which may be used to demonstrate this problem is to capture a grey ramp test chart using multiple exposures. In the portion of the grey ramp test chart corresponding to a transition point between two successive frame exposures, higher levels of luma and chroma noise may be observed. Such noise discontinuity may negatively affect image quality.